fix: add missing required attributes to search tool schemas (#135)

## Summary
- Add `mcp.Required()` to `keyword` in `search_repos` and `search_users` tool schemas
- Add `mcp.Required()` to `org` and `query` in `search_org_teams` tool schema
- Add test verifying required fields are set on all search tool schemas
- Fixes MCP clients failing with `keyword is required` because the schema didn't declare the field as required

Closes #115

---
*This PR was authored by Claude.*

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/135
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <silverwind@noreply.gitea.com>
Co-committed-by: silverwind <silverwind@noreply.gitea.com>

operation/search/search_test.go

@@ -0,0 +1,42 @@
+package search
+
+import (
+	"slices"
+	"testing"
+
+	"github.com/mark3labs/mcp-go/mcp"
+)
+
+func TestSearchToolsRequiredFields(t *testing.T) {
+	tests := []struct {
+		name     string
+		tool     mcp.Tool
+		required []string
+	}{
+		{
+			name:     "search_users",
+			tool:     SearchUsersTool,
+			required: []string{"keyword"},
+		},
+		{
+			name:     "search_org_teams",
+			tool:     SearOrgTeamsTool,
+			required: []string{"org", "query"},
+		},
+		{
+			name:     "search_repos",
+			tool:     SearchReposTool,
+			required: []string{"keyword"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			for _, field := range tt.required {
+				if !slices.Contains(tt.tool.InputSchema.Required, field) {
+					t.Errorf("tool %s: expected %q to be required, got required=%v", tt.name, field, tt.tool.InputSchema.Required)
+				}
+			}
+		})
+	}
+}